Groundwater flow system in Bengal Delta,Bangladesh revealed by environmental isotopes

A total number of 328 groundwater samples are analysed to evaluate the groundwater flow systems in Bengal Delta aquifers, Bangladesh using environmental isotope (²H, ¹⁸O, ¹³C, ³H, and ¹⁴C) techniques. A well-defined Local Meteoric Water Line (LMWL) δ²H = 7.7 δ¹⁸O + 10.7 ‰ is constructed applying linear correlation analyses to the monthly weighted rainfall isotopic compositions (δ¹⁸O and δ²H). The δ¹⁸O and δ²H concentrations of all groundwater samples in the study area are plotted more or less over the LMWL, which provides compelling evidence that all groundwaters are derived from rainfall and floodwater with a minor localized evaporation effects for the shallow groundwaters. Tritium concentration is observed in 40 samples out of 41 with values varying between 0.3 and 5.0 TU, which represents an evidence of young water recharge to the shallow and intermediate aquifers. A decreasing trend of ¹⁴C activity is associated with the heavier δ¹³C values, which indicates the presence of geochemical reactions affecting the ¹⁴C concentration along the groundwater flow system. Both vertical and lateral decrease of ¹⁴C activity toward down gradient show the presence of regional groundwater flow commencing from the unconfined aquifers, which discharges along the coastal regions. Finally, shallow, intermediate, and deep groundwater flow dynamics has revealed in the Bengal Delta aquifers, Bangladesh.     

Assessment of urban groundwater heat contaminant in Jakarta, Indonesia

Urbanization has become one of the domain processes for city development in Indonesia. The results of the extremely high densities of fast growing population have led to negative subsurface environmental impact. Jakarta, as one of the rapidly developed and urbanized cities in Southeast Asia, has become one of the interesting urbanization city to analyze its effects. In Jakarta, the use of groundwater has greatly accelerated conforming to the rise in its population and the development of the industrial sector, which consume a relatively large amount of water. The increase of groundwater exploitation in Jakarta city has already caused a negative impact on these resources. Therefore, an assessment of groundwater trends in the urban area, including their hazard and risk management, is a necessary action. This paper describes the assessment of urban groundwater loading caused by human concentration in Jakarta city. Subsurface heat contamination under the condition of surface warming shows significant effects of urban groundwater loading during the past century in Jakarta city.     

Rapid evolution of the Eocene accretionary complex (Hyuga Group) of the Shimanto terrane in southeastern Kyushu, southwestern Japan

Abstract   Detailed geologic examination of the Eocene accretionary complex (Hyuga Group) of the Shimanto terrane in southeastern Kyushu revealed that the oceanic plate was composed of Paleocene to Lower Eocene mudstone and siliceous mudstone, lower Middle Eocene red mudstone, and mid-Middle Eocene trench-fill turbidite with siltstone breccia, successively overlying the pre-Eocene oceanic plate. This oceanic plate sequence was overlain by Upper Eocene siltstone. Deposition of the lower Middle Eocene red mudstone was accompanied by basalt flows and it is interbedded with continental felsic tuff, which indicates that the basalt and red mudstone were deposited near the trench just before accretion. The Hyuga Group has very similar geological structure to that of the chert–clastic complexes found in the Jurassic accretionary complexes in Japan: that is, a decollement fault formed in the middle of an oceanic plate sequence, and an imbricate structure formed only in the upper part of the sequence. Thus, it appears that the Hyuga Group was formed by the same accretionary process as the Jurassic accretionary complexes. No accretion occurred before the Middle Eocene, and the rapid accretion of the Hyuga Group was commenced by the supply of coarse terrigenous sediments in the mid-Middle Eocene, when the direction of movement of the Pacific Plate changed. The pre-Eocene oceanic basement and lower Middle Eocene volcanic activity suggest that the oceanic plate partly preserved in the Hyuga Group was very similar to the northern part of the present West Philippine Sea Plate.     

钙质石灰岩中桩基轴向承载特性的有限元分析

为了研究钙质石灰岩中桩基的合理设计理论及开发相关的变形破坏数值分析方法,利用弹塑性有限元方法对以硫球石灰岩作为持力层的桩基现场轴向载荷试验进行了数值分析。有限元分析中钙质石灰岩被假定为理想弹塑性材料。结果表明,如果能在有限元解析中合理地考虑桩侧摩阻力的低减效果,弹塑性有限元计算可以较好地模拟与分析钙质砂土中桩基的轴向承载力特性。最后还对开口钢管桩基的土塞效应的发生机制进行了分析。     

Factors affecting dominant peak-flow runoff-generation mechanisms among five neighbouring granitic headwater catchments

We examined how and why dominant peak-flow runoff-generation mechanisms differ among neighbouring headwater catchments. We monitored runoff and groundwater levels and performed terrain analyses in a granitic second-order catchment and its four neighbouring subcatchments in the Kiryu Experimental Watershed in Japan. Our analysis of lag times from peak rainfall to peak runoff suggests differences in the dominant peak-flow runoff-generation mechanisms among the five catchments. For two of the three zero-order catchments, with few perennial groundwater bodies, subsurface flow from hillslopes was the dominant mechanism at some events. However, the dominant mechanisms were channel precipitation and riparian runoff at almost all events in first- and second-order catchments and in the third zero-order catchment, which has a large perennial groundwater body over a bedrock depression in the riparian zone. In this zero-order catchment, the quick-flow ratio was the smallest of the five catchments because subsurface flow from the hillslope was buffered at the riparian zone. These facts suggest that the channel length, riparian buffering, and hillslope connectivity were the factors governing the different dominant peak-flow runoff-generation mechanisms among the catchments. Riparian buffering was affected, not only by surface topography, but also by bedrock topography and bedrock groundwater (BGW) dynamics. Our findings indicate that both of BGW dynamics and topography are important for catchment classification, and the relative importance of topography increases with the change from baseflow to stormflow. Furthermore, mismatching between a geographic source and a flow path resulted in different catchment classifications depending on the approach. Therefore, multiple approaches during both baseflow and stormflow periods are necessary for catchment classification to apply information obtained from one headwater catchment to other headwater catchments within the same region.     

On the effects of compression of a gaseous disc by thermal and dynamical pressures of intergalactic gas

We consider a galaxy moving in a cluster of galaxies and study the effects of compression of the gas disc by both thermal and dynamical pressures of intergalactic gas. As the result of compression, massive gas clouds are formed. They are not stripped by dynamical pressure of the intergalactic gas but stay in the galaxy until they are disrupted by formation of massive stars.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Asteroids approaching the Earth from directions around the Sun

We have estimated close asteroid encounters with the Earth by numerical integrations of a system with the Sun, 9 planets, and 188 near-earth-asteroids during the period 1994–4600. Asteroids approach the Earth from directions within 30 around the Sun in more than 20% of encounters with the closest distance less than 0.01 AU. Since ground-based observations cannot detect these objects, we should develop space-borne and/or lunar observatories in a short time to allow enough warning time before a catastrophic collision.     

Log N — log S of radio sources at 10 GHz with flat spectra

A logN — logS relation at 10 GHz is constructed for sources with the flat spectra 0.5 (flux densitySv ^–) from observations at NRO, MPIfR and others. Based on the source distribution on log (Luminosity) volume plane we obtain an epoch-depending luminosity function which explains the above relation.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.Nobeyama Radio Observatory, a branch of the Tokyo Astronomical Observatory, University of Tokyo, is a facility open for general use by researchers in the field of astronomy and astrophysics.     

Study on the managanese nodule

Chemical and X-ray analyses were performed on the fifteen manganese nodules collected from the Pacific Ocean floor. The results were discussed compared with the previous data on the manganese nodules. Minerals were found to be todorokite, δ-MnO₂ and other silicates, montmorillonite, illite, phillipsite and α-SiO₂. Average composition shows that copper is concentrated on the deep sea nodules more than the shallow ones, and that the todorokite rich nodules contain more copper and nickel than the δ-MnO₂ rich ones. The analyses of fresh water iron-manganese precipitates by bacterial activity suggest that biological process is one of the important factors on the genesis of the sedimentary iron-manganese deposits, including the manganese nodule. The Institute of Physical and Chemical Research